Plunger piston pumps for chainsaws of the basic type described above are known. A plunger piston oil pump is described in German patent document DE-OS 35 27 024. This oil pump comprises a cylindrical pump chamber provided with an intake slot and an outlet slot and a rotatable pump piston plunging into said pump chamber. The pump piston's rotational movement is superposed with a reciprocating movement, whereby the pumping effect is achieved. In this known oil pump it is possible to achieve a dosing of its delivery volume as follows. The surface of the pump piston has an inclined surface that wobbles when the pump piston is rotated, causing the piston to move back and forth in the chamber. The piston can be supported by a stop that is placed at an adjustable distance along the longitudinal axis of the chamber. The supporting means rests transversally to the longitudinal axis of the pump chamber, and is adjustable so as to be axially rigid and radial relative to the pump piston. The adjustable supporting means serves as a means for setting the delivery volume of the piston pump.
A somewhat different type of oil pump is described in German patent document DE-PS 29 45 246. This pump for portable guide rail chain saws has a pump piston mounted in a pump cylinder. The piston executes stroke motions with the aid of a driving means. The pump has an annular groove at its end opposite the driving means, which, via an outlet aperture disposed in the cylindrical wall of a duct, communicates with the pressure duct of the oil pump. An advantage of this oil pump is that pump operation is not interrupted by air being drawn off via the piston shank during the intake phase. Also, the driving unit of the oil pump is supplied with lubricant.
Practically all fields that employ lubricating oil pumps are faced with increasing environmental concerns. Therefore, it is desirable to regulate the delivery volume in order to deliver only the volume of oil necessary in all operating stages.
Previously known pumps regulate the volume of oil delivery by effecting a change in the pump piston stroke. Several examples of this type of volume regulation are known. In one pump, the stop is connected to a set screw that can be turned in a thread which is integral with the casing. By turning the set screw, the stroke of the pump piston is changed. However, in an arrangement of this kind it is difficult to accurately define the minimal and the maximal delivery volumes. Because of the threaded connection between the setting member and the casing, either no defined positions result, or else it is difficult to define positions. Moreover, operating errors are easily possible since, when turning this set screw in the inward or outward direction without having regard to predetermined or preset positions, it is possible to reduce the oil volume inadequately or to increase it excessively.
Another previously described means for adjusting the piston stroke involves a mechanical adjusting mechanism in which the position of the stop is adjusted in its radial distance relative to the central longitudinal axis of the pump piston. This solution does result in a great operational safety. However, the construction of such a device is relatively complicated and, on account of the number of components used, it is not economically optimal.
Another disadvantage of previously described adjusting means arises when one wants to adapt one pump design to several uses. For example, one must design the adjusting mechanism so that it is relatively large in its adjustment range if one wants to use one type of oil pump for several different types of chain saws. The oil requirement in a small chain saw provided for hobby purposes is, of course, quite different from the requirement in a very large chain saw intended for professional application. The present invention solves these and other problems inherent in previously known pumps.